My radial field consists of 55 radials, 75' to 150' in length, buried 0.5" to 1" deep. My coax feedline, encased by a 1.25" gray pvc conduit, is 12'' deep and 80' long. It passes beneath several radials between the shack and the antenna base.
I don't use a common-mode choke at the base feedpoint of my inverted L, where the only matching element is a series-connected capacitor to cancel out the inductive reactance of the antenna's total length of 170'. I am willing to insert a common-mode choke, but don't know what to measure beforehand to learn if one is needed. Nor do I know what changed indications to look for after such a choke has been installed. I'd be grateful for any advice. 73, Charles, W2SH > From: [email protected] > To: [email protected] > Date: Fri, 27 Jan 2012 10:20:16 -0500 > Subject: Re: Topband: T Vertical feed > > > This is a terrible error in logic. Current on the radials will divide > > based on the impedance of each radial. If the feedline happens to be > > a "pathological" length its (outer) shield can carry *all* of the > > antenna return current. > > To Joe's point, I don't think we want the feedline to become a radial. It > also seems that placement of the line should occur under the radial field > and not on top of it, but I have not seen any studies that compare > measurements. Anyone have this data? My initial thought for base-fed > verticals is to use a CM choke at the base and also at the perimeter of the > radial field, unless by placing the line under the field significantly helps > to reduce coupling to the line. > > Paul, W9AC > > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
